Sequence of the 5S rRNA gene fromSinapis alba

Abstract

Total nuclear DNA of S&apis alba (mustard) was digested with the restriction enzyme Bam HI and fractionated on 1 ~o agarose gel, transferred to nitrocellulose filters and hybridized with 32p_ labelled 5S rDNA from rye. A ladder of bands appeared suggesting a tandemly repeated element of 491 bp. The monomer Barn HI DNA band was cloned into pUC 18, and the rDNA clones were selected by colony hybridization. The nucleotide sequence of the 5 S rRNA gene and the intergenic spacer was determined in both directions using the dideoxy sequencing method [6] (Fig. 1). Since the Bam HI site is located inside the 5S rRNA gene, the sequence is aligned starting 34bp upstream from the starting point of the 5S rRNA gene. The position of the presumed coding region (underlined) was inferred by comparing the sequence of the repeat with 5 S rRNA sequences of several species [1, 8]. The length of the coding region is 119 bp, followed by a 21 bp T tract at the 3' end. Comparing the nucleotide sequences of the 5S rDNA repeats of S. alba with Matthiola incana [3], which belongs to the same flowering plant family (Brassicaceae), a 99.2~o homology is found in the 5S rRNA gene region. At the 5S rRNA level the sequence homology to Brassica napus [1] is 99.2~o. One single-base change, C instead ofT, is found as difference between S. and M. incana or B. napus. C in this position is also found in Petunia hybrida [2] and in four Bryophyta species [4]. The repeating length of the M. incana 5S rDNA repeat is 509 bp. The GC content of the intergenic spacer of the 5S rRNA gene is 46.5 ~o for S. alba and 47.2~o for M. incana. The homol-